Email: ohayon@salk.edu

VIDEO 1: Two-Layer Network:

Distributed Stimuli and Multistability

This video shows activity propagation in a 40 x 40 cell, two-layer network (both layers are shown in a single plane). The upper-left graph (A) shows the spatial characteristics of the propagation with activity level indicated on the z axis. The upper right graph (B) is the same data in intensity graph form. The lower figure is the activity trace over time (in iterations).

The network exhibited two types of stable behaviour, depending on the stimulus. The first 8 seconds of the video show the response to repeated single-locus stimuli in which network activity quickly dissipates. At approximately 9 seconds we applied a single pan-network stimulus, simultaneously across the entire network (randomized across units). This single stimulus resulted in the persistent activity seen in the remainder of the clip.

VIDEOS 2 & 3: Propagation of Activity Pre- and Post-Lesion

In the first video (Video #2) we begin with a network that settles even after a pan-network stimulus. These spatially distributed stimulations generate short-term activity that quickly dissipate (this is repeated 5 times).

Video #3 shows that a single stimulation in the post-lesion network can result in a state of persistent activity. Simulations in these spiking models thus confirmed that changes in network structure following localized removal of cells were indeed sufficient to account for the initiation and propagation of hyper-excited oscillatory activity.

VIDEOS 4,5 & 6: Diffuse Micro Lesions and Neurodegeneration

This series shows how varying degrees of cell deletions affect network activity patterns. Cells were deleted randomly in these networks with equal probabilities for both layers. In the first video of this series (# 4) all cells are present and the activity dissipates quickly. The networks with cell deletion probability set at 0.2 (Video #5) and 0.5 (Video #6) both showed a concomitant increase in the creation of localized activity pockets that persisted long after the initial stimulus. The number of loci and the duration of activity both increased with p.

The changes in oscillations and propagation patterns seen following the diffuse removal of cells highlight the importance of examining the contribution of chronic changes in network structure to brain dynamics following neurodegeneration.